The present invention relates generally to the field of natural colouring agents and in particular to a purification process for improving the total yield of curcuminoids in the production of curcuminoid colouring agents e.g. from Curcuma rhizomes. Specifically, there is provided a novel process for obtaining improved yield of curcuminoids by subjecting curcuminoid-containing materials to at least two separation steps, each of which results in commercially valuable colouring agents.
Turmeric or xe2x80x9cyellow rootxe2x80x9d is a general term for plants and plant materials having a high content of curcuminoids, compounds that have a strong colouring effect and which are used extensively in the colouring of e.g. food products. Turmeric plants belong to rhizomatous Curcuma species and have been known for centuries for their flavouring and colouring properties. The plants are grown commercially, particularly in India, but also in Bangladesh, China, Sri Lanka, Indonesia, Taiwan, Haiti, Jamaica and Peru.
It has been found that Curcuma plant materials contain three different curcuminoid compounds including, as the predominant colouring compound, curcumin having a strong yellow colour, and minor yellow and brownish-red components, i.e. the term xe2x80x9ccurcuminoidsxe2x80x9d includes curcumin (C), reddish orange and with two methoxy groups; demothoxy curcumin (DMC), orange-yellow with one methoxy group and bis-demothoxy curcumin (BDMC), yellow and without a methoxy group. The relative proportions of these three curcuminoid components in the source plant material, in particular in the rhizomes, have been reported by several groups. Thus, Perotti (1975) found a ratio of 60:30:10, Krishnamurthy et al. (1976) one of 49:29:22 and Govindarajan (1980) found a ratio of 42:24:34.
The Curcuma rhizomes, including the primary or mother rhizomes and several long cylindrical multi-branced secondary rhizomes growing downward from the primary rhizomes, that contain the curcuminoid compounds in an oily cell phase, are harvested at maturity, typically 8 to 9 months after planting.
After harvest, the rhizomes are cured in a process essentially comprising cooking the fresh rhizomes in water. This cooking step aids in producing a product of fairly uniform colour due to the diffusion of the yellow pigments from the individual oil containing cells into the surrounding tissues. After cooking, the material is spread and allowed to dry in the sun. When properly dried, the rhizomes become hard, almost horny and brittle, and of uniform yellow colour. This cured and dried turmeric product is marketed as bulbs and fingers, each type in polished and unpolished forms. This turmeric raw material is then made available to bulk purchase as a starting material for further processing resulting in commercial colouring agents.
Preparing more or less purified solvent extracts of Curcuma plant materials, in particular rhizomes as described above, provides commercial curcuminoid-containing colouring agents or compositions. Traditionally, methods for the isolation of curcuminoid colours from the Curcuma starting material involve conventional extraction methods typically using solvents of defined purity allowed by national and international food laws for the processing of food additives, and optionally further purification step(s).
The curcuminoid-containing phase that is obtained by the above extraction methods is in the form of an oleoresin comprising an essential oil containing the curcuminoids. The curcuminoid content of the oleoresin is typically in the range of 30-50% by weight. However, the essential oil fraction of the oleoresin has a very strong and bitter flavour, which for many purposes, such as colouring of food products, is undesirable. In order to meet the increasing demand for a highly concentrated flavour-free curcuminoid product, the oleoresin may be processed further. Thus, the oleoresin may subsequently be subjected to a crystallisation step resulting in the obtainment of a curcuminoid powder of a relatively high purity (typically  greater than 90% by weight) in respect of curcuminoids. The maximum yield of curcuminoids that can be obtained in this conventional process including the crystallisation step is about 60% by weight, i.e. only about 60% of the curcuminoids initially present in the oleoresin starting material is recovered in the crystal-containing powder.
The residual material that remains after the above separation of curcuminoid crystals consists mainly of the essential oil fraction of the oleoresin and a relatively high proportion of the curcuminoids initially present in the oleoresin, i.e. 40% by weight or more. However, this residual material, although it has a content of curcuminoids that confers to the residual material a yellowish colour, is unsuitable as a colouring agent, not only due to the extensive undesirable flavour, but also due to its relatively low colouring effect. Furthermore, the residual material as such is not directly applicable in e.g. food products. Presently, this residual material is, for these reasons, not utilised commercially and it therefore represents a substantial waste of curcuminoid colouring material. Evidently, this waste of curcumoids in the conventional process for providing concentrated and flavour-free curminoid (or xe2x80x9cturmericxe2x80x9d) colouring agents or compositions adds significantly to the costs of providing such highly desirable products.
A strong industrial need therefore exists to render processes for providing such useful, and/or pure and concentrated high quality curcuminoid products economically feasible. This has been achieved by the present invention which is based on the discovery that the curcuminoid-containing waste material can be utilised as a starting material for commercially valuable novel curcuminoid colouring agents having excellent and particular colouring properties and, relative to commercial oleoresin products, a similar or even reduced content of undesired flavouring compounds.
Accordingly, the present invention pertains in a first aspect to a process for obtaining an improved total yield of curcuminoid colouring agent, the method comprising the steps of (i) providing a curcuminoid-containing material, (ii) subjecting said material to a first separation step so as to obtain a curcuminoid-containing phase and a first residue, (iii) subjecting said phase to curcuminoid crystallisation conditions, (iv) harvesting the thus formed crystals so as to obtain a first curcuminoid colouring agent in the form of curcuminoid crystals, and a second residue containing curcuminoids in non-crystalline form, (v) subjecting said second residue to a second separation step to obtain a second curcuminoid colouring agent, and a third residue.
In another aspect, the invention provides a colouring agent containing curcumin, demethoxy curcumin and bis-demethoxy curcumin, the agent is obtainable, as a second curcuminoid colouring agent, by the above process, the combined amounts of demethoxy curcumin and bis-demethoxy curcumin being above 50% of the total amount of curcuminoids.
A major objective of the present invention is to provide a process for obtaining an improved total yield of curcuminoids for use as commercially valuable curcuminoid colouring agents. As used herein the expression xe2x80x9ccurcuminoid colouring agentxe2x80x9d includes a xe2x80x9ccolouring agentxe2x80x9d or a xe2x80x9ccolouring compositionxe2x80x9d containing at least one curcuminoid compound including a compound selected from the group consisting of curcumin, demethoxy curcumin and bis-demethoxy curcumin. Furthermore, the xe2x80x9ccurcuminoid colouring agentxe2x80x9d may be obtainable after a first and/or a second separation step of the provided curcuminoid-containing material. Typically, a commercially valuable colouring agent contains at least 30% by weight of the curcuminoids. Alternatively, the colouring agent may contain any suitable auxiliary compound e.g. emulsifiers, so as to become suitable for specific application e.g. as a food colouring composition.
The process of the present invention involves in a first step that a curcuminoid-containing material is provided. As used herein, the expression xe2x80x9ccurcuminoid-containing materialxe2x80x9d includes material derived from any prokaryotic and/or eukaryotic species containing at least one curcuminoid. Preferably, curcuminoid-containing material derived from eukaryotic species is derived from plant species. Such plant species include cultivated or wild plants. In one embodiment of the present invention the plant species include plants of the genus Curcuma. Useful curcuminoid producing species of this genus include Curcuma longa L., C. aromatica Salisb., C. amada Roxb., C. zedoaria Rosc. and C. xanthorrhiza Roxb.
The plant material is advantageously treated in a way so as to provide the curcuminoids in a uniform and easily accessible condition. Such treatments include boiling, curing and subsequent drying of the curcuminoid-containing plant material prior to separation of the curcuminoids. The plant starting material can be divided into particles prior to the first separation step.
It is also possible to provide curcuminoid-containing materials by subjecting wild type curcuminoid-containing organisms to a mutagenisation treatment and select a strain that is capable of producing excess amount of one or more of the curcuminoids or a strain capable of producing curcuminoids in a different ratio as compared to the parent strain. The use of microorganisms or plants that have been genetically modified to produce curcuminoids as starting material is also contemplated.
A curcuminoid-containing starting material can be selected that has one of the curcuminoids e.g. curcumin as the predominant curcuminoid. Additionally, curcuminoid-containing starting material may be provided by mixing curcuminoid-containing material that is derived from different sources as defined above.
The first separation step in the process of the present invention includes any separation procedure resulting in a phase containing the bulk of the curcuminoid compounds of the curcuminoid-containing material i.e. a curcuminoid-containing phase, and a phase essentially comprising waste matter i.e. a first residue, of the curcuminoid-containing material. Where the curcuminoid-containing material is a plant material the first residue will be the plant matter devoid of the curcuminoids. A separation procedure as used in the present process is typically selected from the group consisting of a precipitation, an extraction, a filtration and a distillation. In a preferred embodiment the separation step is an extraction performed by adding one or more organic solvents to the curcuminoid-containing material. In the present context an extraction may also include a super-critical extraction using carbon dioxide as a solvent. After extraction the phases can be separated by e.g. filtering, to obtain the two above phases.
Adding any suitable solvent to the curcuminoid-containing material as defined above can carry out an extraction. Suitable solvents include aromatic hydrocarbons, aliphatic hydrocarbons such as petroleum ether, heptane, pentane, hexane; chlorinated hydrocarbons such as ethylene dichloride, dichloromethane, trichloro-ethylene; ketones such as acetone; esters such as ethylacetate; alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol and n-butanol. It is contemplated that the first and second separation step of the present invention also encompasses the use of any mixture of solvents.
According to the invention, the resulting curcuminoid-containing phase may be in any form including a liquid form, a semi-liquid form and a solid form. Preferably, the curcuminoid-containing phase is in a semi-liquid form characterised as an oleoresin comprising an essential oil fraction containing the curcuminoids. Accordingly, the curcuminoids are dispersed in an oily phase. This curcuminoid-containing phase is the traditional colouring and flavouring product used as described hereinbefore. Although some of the curcuminoids initially present in the plant are retained in the first residue the colour content of the oleoresin is defined as being 100% for the purpose of subsequent calculations of yield in the further processing of the curcuminoid containing phase. The curcuminoids in the oleoresin is, however, diluted by the presence of the oily phase, and presence of impurities. Accordingly, the purity, or strength, of the oleoresin is about 40% by weight (in the following, all percentages are by weight unless otherwise stated). In the present context the term xe2x80x9cpurexe2x80x9d, xe2x80x9cpurityxe2x80x9d or xe2x80x9cstrengthxe2x80x9d refers to the content by weight of curcuminoids in the sample.
In one embodiment of the present invention curcumin is the predominant curcuminoid in the curcuminoid-containing phase. The ratio of the three curcuminoids in the curcuminoid-containing phase is typically: curcumin about 50-70%, demethoxy curcumin about 10-30% and bis-demethoxy curcumin about 10-30% the sum of the three compounds being 100%.
In order to obtain a highly concentrated flavour-free curcuminoid product, the curcuminoid-containing phase (oleoresin) is processed further. The curcuminoid-containing phase obtained by the process of the present invention is subjected to curcuminoid separation conditions typically a crystallisation step, resulting in a curcuminoid powder. Such a separation is a classic separation procedure, which also include a precipitation, a centrifugation, a filtration and a distillation. The person of skill in the art can easily select an optimal method for this purpose.
After subjecting the curcuminoid-containing phase to crystallisation conditions the formed crystals are harvested as a curcuminoid powder whereby a first curcuminoid colouring agent is formed. This first curcuminoid colouring agent is a powder preferably having, in respect of curcuminoids, a purity of at least 70% such as at least 80%, 85%, 90% or more preferably a purity of at least 95% or even 99%. The first curcuminoid colouring agent is further characterised in having a typical ratio (as defined above) of the three curcuminoids in the curcumin powder: curcumin about 65-85%, demethoxy curcumin about 10-30% and bis-demethoxy curcumin about 5-15%, the sum of the three compounds being 100%. The yield of this process is about 60% of the cuminoids initially present in the curcuminoid-containing phase (oleoresin).
During the crystallisation process the oily phase, flavouring compounds and any impurities remain in solution together with the remaining curcuminoids. This remaining solution is characterised as xe2x80x9ca second residuexe2x80x9d containing curcuminoids in a non-crystalline form. Currently, this second residue is considered a waste due to its very limited commercial value.
The improvement provided by the present invention is to obtain a commercially valuable second curcuminoid colouring agent by subjecting this second residue to a second separation step.
The second residue is in a form selected from a liquid form, a semi-liquid form and a solid form. The content of curcuminoids is typically at least 30% of the curcuminoids initially present in the oleoresin such as at least 35% including at least 40% or at least 50%, or even more if the crystallisation step has not been performed under optimal conditions.
In accordance with the invention, the second residue is subjected to a second separation step, which may be carried out using any known extraction method, and extraction solvent as described hereinbefore. In one embodiment, extraction of the second residue is performed with hexane as the solvent of choice. Preferably, hexane is applied at a temperature in the range 10-30xc2x0 C. e.g. about 20xc2x0 C., optionally under stirring of the solution.
The second separation step results in a second curcuminoid colouring agent. This colouring agent can be in a liquid, a semi-liquid or a solid form. Most preferably, the second curcuminoid colouring agent is in a solid form as a xe2x80x9cHigh purityxe2x80x9d curcuminoid powder. The xe2x80x9cHigh purityxe2x80x9d curcuminoid colouring agent contains the three above curcuminoid compounds. The ratio of the three compounds in the curcuminoid-containing phase is typically: curcumin about 35-49%, demethoxy curcumin about 20-30% and bis-demethoxy curcumin about 20-30%, the sum of the three compounds being 100%.
The xe2x80x9cHigh purityxe2x80x9d curcuminoid colouring agent has a purity by weight of curcuminoids as compared to the second residue including a purity of at least 25%, such as at least 30% including at least 40% or even at least 50%. The total yield of curcuminoids is improved by at least 25% of the curcuminoids initially present in the curcuminoid-containing phase (oleoresin) such as at least 30%, 35% or even preferably at least 40% of the curcuminoids initially present in the curcuminoid-containing phase (oleoresin). It is contemplated that the xe2x80x9cHigh purityxe2x80x9d curcuminoid colouring agent may be diluted to any desired extend using any suitable dilution agent.
The second separation step as described above may alternatively be performed as a liquid: liquid extraction using e.g. methanol and hexane. Methanol is applied to the second residue to form a mixture which can be extracted by stepwise adding of hexane to the mixture and subsequent separation of the two phases formed. Preferably an emulsifier is added to the resulting methanol phase containing the curcuminoids. It is however contemplated that any auxiliary agent as described below can be used. After evaporation of the solvent phase a second curcuminoid colouring agent is formed. This second curcuminoid colouring agent can be in a liquid and semi-liquid state and is characterized as being water/oil soluble/dispersible and hence xe2x80x9cReady to usexe2x80x9d.
Auxiliary agents for use subsequent to the liquid:liquid extraction may be any agent useful in conferring a desired property to the xe2x80x9cReady to usexe2x80x9d curcuminoid colouring agent. Desired properties include e.g. solubility properties useful for specific applications. Examples of useful auxiliary agents include, but are not limited to oils and emulsifiers. A useful auxiliary agent is a food grade emulsifier such as Lecithin, Sorbitan derivatives, Polysorbate or additives like glycerol and Propylene glycol.
The xe2x80x9cReady to usexe2x80x9d curcuminoid colouring agent contains the three previously described curcuminoid compounds. The ratio of the three compounds is identical to the ratio as described above for the second curcuminoid colouring agent. The purity of the xe2x80x9cReady to usexe2x80x9d curcuminoid colouring agent is dependent on the amount of an auxiliary agent added in the alternative extraction and may be of a purity in the range of 0,25%-40% by weight of curcuminoids as compared to the second residue. However, the total yield of curcuminoids by using the liquid:liquid extraction is comparable to the yield obtained for the second curcuminoid colouring agent i.e. the total yield of curcuminoids is improved by at least 25% of the curcuminoids initially present in the curcuminoid-containing phase (oleoresin) as defined hereinbefore.
In accordance with the invention, the second separation step results in a third liquid residue, essentially void of curcuminoids. This third residue contains the major part of flavouring compounds of the turmeric oleoresin. For certain applications this third residue is useful as a flavouring compound. Furthermore, the third residue is valuable as a medicament or for use in the manufacturing of a medicament e.g. for treating infectious diseases. It is further contemplated that the third residue is useful as a preserving agent e.g. in the preservation of food products or pharmaceuticals.
It is another objective of the present invention to provide a novel colouring agent containing curcumin, demethoxy curcumin and bis-demethoxy curcumin. The colouring agent is obtainable as a second curcuminoid colouring agent, by the process of the invention and the combined amount of demethoxy curcumin and bis-demethoxy is typically about 50-70% by weight of the total amount of curcuminoids, such as at least 50%, at least 55%, at least 60%, or at least 70%. This novel colouring agent may be used directly for colouring purposes as defined below. Furthermore, it is to be understood that the features of the colouring composition as described below applies for the novel colouring agent as well.
A composition comprising such a colouring agent is also encompassed by the present invention. Such a composition may comprise a further colouring agent selected from a natural and/or a synthetic colouring agent. Synthetic colouring agents are normally very pure chemicals with standardised colouring strength. The colours are available as powders, pastes, granules and solutions and may include compounds e.g. selected from Brillant black, Brown FK, Fast Green, Sunset yellow, Carmoisine and Indigo carmine.
Commercially available natural colouring agents are mixtures of pigments found in nature. Common natural colours include flavonoids, carotenoids, Betalaine pigments, quininoid pigments, porphyrin pigments and malanoidin pigments.
The synthetic as well as the natural colours may be provided as lakes e.g. as aluminium chelates produced by reacting solutions of the colours with freshly prepared alumina. In general, such lakes have enhanced light stability over the soluble dye and can be used for colouring dry powder products.
The composition of the invention may e.g. be encapsulated as described in WO 97/26802 and WO 97/26803 which is hereby incorporated by reference. By this encapsulation, the composition may be applied in environments which are normally considered as unfavourable for non-encapsulated pigments such as e.g. hydrophobic pigments in aqueous environments. Furthermore, the encapsulation provides a form wherein the composition essentially does not migrate from one to another compartment e.g. in foodstuffs. In one embodiment of the present invention the further colouring agent may be a curcuminoid such as e.g. the first curcuminoid colouring agent obtained by the process of the present invention.
In a further aspect the invention pertains to the use of a composition according to the invention as a colouring agent in the manufacturing of an edible product. As used herein, the expression xe2x80x9cedible productxe2x80x9d denotes any solid or liquid food product. Edible products include the product types referred to as xe2x80x9cnutraceuticalsxe2x80x9d, xe2x80x9cfunctional foodsxe2x80x9d or xe2x80x9chealth improving foodsxe2x80x9d; i.e. food products or food supplements comprising components that are considered to confer certain health improving characteristics. Such products may be in any conventional form including products in tablet or capsule dosage forms that may comprise separate compartments which can be coloured separately. It will be appreciated that when a composition according to the invention is used in the manufacturing of such a nutraceutical products, the colouring substance can, in addition to its colouring effect, also confer to such products a nutritionally and/or health improving effect. Such health improving effects are well described in the art and include antioxidant activities,
In other useful embodiments, the composition of the invention is used in the manufacturing of an antiseptic or antimicrobial compound, optionally by including the third residue in the composition. The term xe2x80x9cantimicrobial compoundxe2x80x9d includes agents that kill micro-organisms (bactericidal) or inhibit the growth (bacteriostatic) of microorganisms.
In a further useful embodiment, the composition according to the invention is used for the colouring of textiles or polymers. In the present context the term xe2x80x9ctextilexe2x80x9d refers to any filament, fibre or yarn that can be made into fabric or cloth and used in e.g. wearing apparel, household linens and beddings, upholstery, draperies and curtains, wall coverings, rugs and carpets.